Commit c818a181 authored by Andi Kleen's avatar Andi Kleen Committed by Linus Torvalds
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[PATCH] x86_64: On Intel CPUs don't do an additional CPU sync before RDTSC



RDTSC serialization using cpuid is not needed for Intel platforms.
This increases gettimeofday performance.

Cc: vojtech@suse.cz
Cc: rohit.seth@intel.com
Signed-off-by: default avatarAndi Kleen <ak@suse.de>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 7f6c5b04
......@@ -1042,6 +1042,7 @@ static void __cpuinit init_intel(struct cpuinfo_x86 *c)
if ((c->x86 == 0xf && c->x86_model >= 0x03) ||
(c->x86 == 0x6 && c->x86_model >= 0x0e))
set_bit(X86_FEATURE_CONSTANT_TSC, &c->x86_capability);
set_bit(X86_FEATURE_SYNC_RDTSC, &c->x86_capability);
c->x86_max_cores = intel_num_cpu_cores(c);
srat_detect_node();
......
......@@ -71,14 +71,6 @@ unsigned long __wall_jiffies __section_wall_jiffies = INITIAL_JIFFIES;
struct timespec __xtime __section_xtime;
struct timezone __sys_tz __section_sys_tz;
static inline void rdtscll_sync(unsigned long *tsc)
{
#ifdef CONFIG_SMP
sync_core();
#endif
rdtscll(*tsc);
}
/*
* do_gettimeoffset() returns microseconds since last timer interrupt was
* triggered by hardware. A memory read of HPET is slower than a register read
......@@ -93,7 +85,7 @@ static inline unsigned int do_gettimeoffset_tsc(void)
{
unsigned long t;
unsigned long x;
rdtscll_sync(&t);
t = get_cycles_sync();
if (t < vxtime.last_tsc) t = vxtime.last_tsc; /* hack */
x = ((t - vxtime.last_tsc) * vxtime.tsc_quot) >> 32;
return x;
......@@ -309,8 +301,7 @@ unsigned long long monotonic_clock(void)
last_offset = vxtime.last_tsc;
base = monotonic_base;
} while (read_seqretry(&xtime_lock, seq));
sync_core();
rdtscll(this_offset);
this_offset = get_cycles_sync();
offset = (this_offset - last_offset)*1000/cpu_khz;
return base + offset;
}
......@@ -391,7 +382,7 @@ static irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
delay = LATCH - 1 - delay;
}
rdtscll_sync(&tsc);
tsc = get_cycles_sync();
if (vxtime.mode == VXTIME_HPET) {
if (offset - vxtime.last > hpet_tick) {
......@@ -700,8 +691,7 @@ static unsigned int __init hpet_calibrate_tsc(void)
do {
local_irq_disable();
hpet_now = hpet_readl(HPET_COUNTER);
sync_core();
rdtscl(tsc_now);
tsc_now = get_cycles_sync();
local_irq_restore(flags);
} while ((tsc_now - tsc_start) < TICK_COUNT &&
(hpet_now - hpet_start) < TICK_COUNT);
......@@ -731,11 +721,9 @@ static unsigned int __init pit_calibrate_tsc(void)
outb(0xb0, 0x43);
outb((PIT_TICK_RATE / (1000 / 50)) & 0xff, 0x42);
outb((PIT_TICK_RATE / (1000 / 50)) >> 8, 0x42);
rdtscll(start);
sync_core();
start = get_cycles_sync();
while ((inb(0x61) & 0x20) == 0);
sync_core();
rdtscll(end);
end = get_cycles_sync();
spin_unlock_irqrestore(&i8253_lock, flags);
......@@ -939,7 +927,7 @@ void __init time_init(void)
vxtime.mode = VXTIME_TSC;
vxtime.quot = (1000000L << 32) / vxtime_hz;
vxtime.tsc_quot = (1000L << 32) / cpu_khz;
rdtscll_sync(&vxtime.last_tsc);
vxtime.last_tsc = get_cycles_sync();
setup_irq(0, &irq0);
set_cyc2ns_scale(cpu_khz);
......
......@@ -66,8 +66,7 @@ static force_inline void do_vgettimeofday(struct timeval * tv)
(__jiffies - __wall_jiffies) * (1000000 / HZ);
if (__vxtime.mode != VXTIME_HPET) {
sync_core();
rdtscll(t);
t = get_cycles_sync();
if (t < __vxtime.last_tsc)
t = __vxtime.last_tsc;
usec += ((t - __vxtime.last_tsc) *
......
......@@ -63,6 +63,7 @@
#define X86_FEATURE_CENTAUR_MCR (3*32+ 3) /* Centaur MCRs (= MTRRs) */
#define X86_FEATURE_K8_C (3*32+ 4) /* C stepping K8 */
#define X86_FEATURE_CONSTANT_TSC (3*32+5) /* TSC runs at constant rate */
#define X86_FEATURE_SYNC_RDTSC (3*32+6) /* RDTSC syncs CPU core */
/* Intel-defined CPU features, CPUID level 0x00000001 (ecx), word 4 */
#define X86_FEATURE_XMM3 (4*32+ 0) /* Streaming SIMD Extensions-3 */
......
......@@ -10,6 +10,9 @@
#include <asm/msr.h>
#include <asm/vsyscall.h>
#include <asm/hpet.h>
#include <asm/system.h>
#include <asm/processor.h>
#include <linux/compiler.h>
#define CLOCK_TICK_RATE PIT_TICK_RATE /* Underlying HZ */
......@@ -23,6 +26,19 @@ static inline cycles_t get_cycles (void)
return ret;
}
/* Like get_cycles, but make sure the CPU is synchronized. */
static __always_inline cycles_t get_cycles_sync(void)
{
unsigned long long ret;
unsigned eax;
/* Don't do an additional sync on CPUs where we know
RDTSC is already synchronous. */
alternative_io(ASM_NOP2, "cpuid", X86_FEATURE_SYNC_RDTSC,
"=a" (eax), "0" (1) : "ebx","ecx","edx","memory");
rdtscll(ret);
return ret;
}
extern unsigned int cpu_khz;
extern int read_current_timer(unsigned long *timer_value);
......
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